1. Field of the Invention
This invention relates to the melting of raw materials to make molten glass and particularly relates to the modification and use of glass melting furnaces which employ combustion as a source of heat for melting glass batch materials. In particular, this invention relates to improvements in waste heat recovery systems for preheating glass batch materials.
2. Brief Description of the Prior Art
Glassmaking furnaces employing combustion as a significant or primary source of heat for melting glass batch materials have in the past included facilities for recovering waste heat from the gaseous effluence exhausted from such furnaces and transferring a portion of that heat to unmelted glass batch materials before feeding them into the glass melting furnace. U.S. Pat. No. 3,788,832 to Nesbitt et al and U.S. Pat. No. 3,880,639 to Bodner et al both relate to the preheating of agglomerated glass batch materials by direct contact with a gaseous effluent being exhausted from a glass melting furnace. While pulverulent glass batch materials also could be contacted directly by hot exhaust gases to preheat them, direct contact by rapidly flowing gases would tend to fluidize the fine batch materials causing segregation of the batch ingredients according to particle size and also causing the discharge of extremely fine particulate batch materials with the exhaust gases. In order to overcome such particulate discharge it would be necessary to provide dust bags, cyclones or some like pollution abatement device.
U.S. Pat. No. 3,185,554 to Sweo et al is related to a method of preheating glass batch materials by independent heating means other than exhausted effluent so that there is no unpredictable relationship between varying amounts of waste heat and the amount of heat provided for preheating unmelted batch material. There is, of course, no direct contact between the heating means of Sweo et al and the effluent exhausted from the furnace disclosed in that patent.
One can contemplate systems for recovering waste heat from the exhausted effluent of a glass melting furnace and using that heat to preheat glass batch materials which do not provide for direct contact between the exhausted effluent and the glass batch materials. Those familiar with the glassmaking art may readily contemplate such systems as being analogous to the regenerative or recuperative systems employed for preheating incoming combustion air with heat recovered from exhausted effluent. There are drawbacks, however, which would be associated with such systems. For one, the efficiency of heat transfer for such a system would be relatively low. For another, the material handling problems of passing a solid, powdery material through or over the same devices would serve as heat capacitors to hold the heat acquired from exhausted effluent would be difficult to operate without encountering, clogging and sticking of glass batch materials on the hot surfaces, particularly at the initiation of a batch input cycle.
The present invention contemplates heat transfer method and apparatus for utilizing waste heat to preheat glass batch materials while avoiding direct contact between effluent gases and powdery or agglomerated glass batch materials.